Previously, "555" NXX calls were dedicated for directory assistance services. For example, a "555-1212" call provides directory assistance within a calling party's area code, and a "NPA-555-1212" call provides directory assistance within another area code depending on a local dialing plan.
The Industry Numbering Committee (INC) approved guidelines to broaden the assignment of 555 NXX line numbers in a document entitled, 555 NXX Assignment Guidelines, INC#94-0429-002. These guidelines enable the assignment of 555 numbers on either a national basis or a non-national basis. In accordance with these guidelines, the number 555-1212 is considered unassignable for any purpose other than directory assistance services provided by interexchange and local exchange carriers. In addition, a block of one hundred 555 line numbers from 555-0100 to 555-0199 are reserved as fictitious non-working numbers for use by the entertainment and advertising industries. Other 555 numbers also have been grandfathered.
Using these guidelines, many enhanced service providers, information providers, and businesses have requested and been assigned 555 numbers for their use. As of June 1996, 2,143 numbers have been assigned of the available 555 numbers. Of these assigned numbers, 1,785 (83%) numbers are national numbers. The industry expectation is a 7 digit dialed 555 number.